Diseases of the Respiratory System - Respiratory diseases caused by
fungi

Two fungal diseases affecting respiration are of great importance in
particular regions of the United States. They are both caused by types
of fungi capable of growing within mammalian tissue, thereby infecting
and destroying it. Both cause chronic diseases very similar to
tuberculosis and may lead to death, though that is a far less common
outcome—even when untreated—than in tuberculosis.

The spores of the fungi are inhaled from the air, and the response of
the body is similar to that in tuberculosis in that most people become
merely infected (the spores being contained by body defenses) while a
few develop progressive disease. The body also produces antibodies, and
consequently skin tests similar to the tuberculin test can identify
infected individuals.

Histoplasmosis
(named for a fungus called
histoplasma
) organisms are prevalent in the Midwest, generally in the areas of the
Ohio, Mississippi, and Missouri rivers. Largely unknown prior to World
War II, histoplasmosis has been studied extensively since. Local
epidemics have brought it to public attention on several occasions. The
fungus grows readily in soil containing large amounts of bird (chickens,
pigeons, starlings) or bat excrement. One of the better ways to assure
exposure is to clean out an old chicken coop. The concentration of
organisms may reach such high levels in bat caves that entry by
spelunkers may prove fatal. In contrast to tuberculosis, the amount of
exposure seems to play a very important role in determining the extent
of the disease. There also seem to be few cases of late breakdown (the
rule in tuberculosis). Most people develop the active disease, if at
all, at the time of their initial exposure.

Coccidioidomycosis
(for
Coccidioides
fungus) also generates in the soil, in this case in California, the
southwest United States, and Mexico. It grows best in hot, dry soil. The
common names for this disease are
desert rheumatism
or
valley fever
. Infection and disease occur in a similar pattern to that of
histoplasmosis. Skin testing of large population groups for both these
fungi in the appropriate geographical areas indicates that the majority
of exposed individuals quite adequately contain the initial infection
and never develop any illness or active disease.

Because Americans travel into infected regions, these diseases are being
seen more frequently in people who do not live where the fungi are
found. Both conditions, fortunately, are often self-limited, even when
active disease develops. For more severe cases there is a drug,
amphotericin-B
, which is quite effective; however, because it is also quite toxic to
the patient, it must be given in progressive doses starting with a small
initial dose, to permit the body's tolerance to build up. It is
hoped that less toxic agents will be found in the future that will be
just as effective against the fungus.